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lecture_questions_prelim2_key

# lecture_questions_prelim2_key - A ball of mass m is swung...

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A ball of mass m is swung at the end of the rope in a horizontal circle . Its speed v is constant and the length of the rope is L . What work W is done by the tension T in the rope when the mass moves a small distance s along the circle? L s v W = ? A. mg s B. T s C. T L D. 0

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10 kg F pull =10 N 10 ° 10 m A 10 kg crate is pulled 10 m along a frictionless horizontal floor by a force F pull =10 N applied at an angle of 10 ° with respect to the horizontal, as shown. What is the net work done on the crate by all the forces that act on it? W net = ? A. 100 cos 10 ° J B. 100 sin 10 ° J C. 1000 J+ 100 sin 10 ° J D. 1000 J+ 100 sin 10 ° J
A car of mass m traveling at a speed v is braked to a stop by a constant force F . What is the stopping distance d of the car? (Use energy/work concepts to solve, not NII.) d = ? A. F/v B. mv/F C. mv 2 /2F D. mv 2 /F E. 2F/mv 2

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A car of mass m traveling at a speed v is braked to a stop by a constant force F . If the initial speed of the car is doubled , by what factor does its stopping distance d change ? d(2v)/d(v) = ? A. 1/4 B. 1/2 C. 1 D. 2 E. 4
The maximum braking force F is equal to the maximum static friction force of the road on the tires. If the mass m of the car is doubled, by what factor does its stopping distance change? d(2m)/d(m) = ? A. 1/4 B. 1/2 C. 1 D. 2 E. 4

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A pig has a choice of three different frictionless slides as shown. With which slide will the pig reach the ground with the greatest speed? (Think about the work done on the pig by the pig's weight.) A. (a) B. (b) C. (c) D. all the same
A pig has a choice of three different frictionless slides as shown. With which slide will the pig reach the ground in the least time? A. (a) B. (b) C. (c) D. all the same E. not enough information

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A toy gun has a spring with spring constant k =100 N/m . The spring is compressed a distance of 10 cm and a ball of mass m =10 g is inserted in the gun. After the trigger releases the spring, what will be the ball's speed v when the spring has returned to its equilibrium length? v=? A. 1 m/s B. 5 m/s C. 10 m/s D. 50 m/s E. none of the above
A cyclist travels along a flat road at constant speed v. The power produced by the cyclist all goes to overcoming air drag . How does the power the cyclist must produce to travel at 54 km/h compare with that required to travel at 27 km/h ? P(54 km/h)/P(27 km/h) = ? A. 1 B. 2 C. 4 D. 8 E. 16

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An SUV of mass m=2000 kg drives down Buffalo St. at a constant speed v=15 m/s (about 30 mi/h). Take the angle of Buffalo St. as 6 ° , and sin(6 ° ) 0.1. In order for the car to travel at constant speed, what power must be removed from the car to cancel the power delivered to it by gravity? (This power is associated with the force of the road on the car's tires, but ultimately is dissipated in the car's brakes.) P ? A. 1 kW B. 3 kW C. 10 kW D. 30 kW E. 100 kW
Which of the following forces are conservative forces?

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